# std::unexpected

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< cpp‎ | error

Defined in header `<exception>` |  |
void unexpected(); |  | (until C++11)
[[noreturn]] void unexpected(); |  | (deprecated in C++11) (removed in C++17)

`std::unexpected()` is called by the C++ runtime when a dynamic exception specification is violated: an exception is thrown from a function whose exception specification forbids exceptions of this type.

`std::unexpected()` may also be called directly from the program.

In either case, `std::unexpected` calls the currently installed std::unexpected_handler. The default std::unexpected_handler calls std::terminate.

If a destructor reset the unexpected handler during stack unwinding and the unwinding later led to `unexpected` being called, the handler that was installed at the end of the throw expression is the one that will be called (note: it was ambiguous whether re-throwing applied the new handlers). | (until C++11)
If a destructor reset the unexpected handler during stack unwinding, it is unspecified which handler is called if the unwinding later led to `unexpected` being called. | (since C++11)

### Exceptions

Throw any exception thrown by the currently installed std::unexpected_handler.

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2111 | C++11 | effect of calling std::set_unexpected during stack unwinding differs from C++98 and breaks some ABIs | made unspecified

### See also

unexpected (C++23) | represented as an unexpected value (class template)
unexpected_handler (deprecated in C++11)(removed in C++17) | the type of the function called by std::unexpected (typedef)

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